Manufacturers of electronic circuits such as power supplies often need to include power factor correction circuitry along with the remainder of the power supply circuitry. A power factor corrector requires a circuit capable of squaring an analog voltage.
Prior art attempts at squaring an analog voltage include a log/antilog circuit. This implementation requires the circuit to take the natural logarithm of the voltage, multiply it by two, then take the inverse natural logarithm of the result. This type of circuit is complex, consumes a considerable amount of power, is slow, and is susceptible to many errors due to component matching, thermal gradients, and large signal non-linearities. Such a device is disclosed in National Semiconductor Corp. Applications Note #31, Jun., 1986 Revision, Page 19.
Another approach at providing an analog squaring circuit is shown in U.S. Pat. No. 4,677,366 wherein two resistors along with a zener diode across one resistor implement a rudimentary, one breakpoint, linear approximation of a squaring function. This method, however, is inherently inaccurate due to temperature drift characteristics of the zener diode. Most importantly, the dynamic range and accuracy of this method is dependent upon the breakdown voltage of the zener diode. Given that the lowest useful zener diode voltage is approximately 4.7 volts, a two breakpoint squaring approximation would require an input voltage of greater than approximately ten volts. An even more accurate squaring function approximation would require an even larger input signal.